Ab-initio calculatons of hydrogen embrittlement in high strength steels

Trabajo presentado en el International RILEM Conference on Advances in Construction Materials Through Science and Engineering, celebrado en Hong Kong (China), del 5 al 7 de septiembreHydrogen embrittlement is believed to be one of the main reasons for cracking of metals under stress. High strength steels in these structures often include a ferritic core made of alpha-iron (body centered cubic lattice). Previous work was concerned with the interaction of atomic hydrogen with iron using first principles calculations. We studied the effect of interstitial hydrogen in the iron lattice and the stress induced by the interstitial hydrogen in the host lattice. In this paper we show the dynamical behaviour of hydrogen inside the iron lattice. Using abinitio Molecular Dynamics and by taking statistical averages diffusion coefficients hydrogen diffusion paths are obtained. Depending on temperature, the diffusion path involve going through tetrahedral or octahedral sites. Simulations where a number of hydrogens occasionally meet in one unit cell have been performed to elucidate the effect of interactions between hydrogens. From simulated diffusion path, the diffusion coefficient is calculated from Einstein´s equation. We also show the Fe-Fe interaction weakens. Iron Debye temperature decreases monotonically for increasing concentration of interstitial hydrogen, proving that iron-iron interatomic potential is significantly weakened in the presence of a large number of diffusing hydrogen atoms